Rapid protection system for freshly-placed concrete and a method of practicing the system

ABSTRACT

A system and method for the rapid protection of freshly placed concrete. The system includes a mat which extends the full width of the freshly placed concrete and is mounted to be displaced and positioned so that it is located at approximately 4 inches above the top surface of the freshly placed concrete for a set period of time and then placed on the top surface of the freshly placed concrete for a further set period of time.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application relies on priority from provisional application,No. 60/323,094, which was filed on Sep. 19, 2001.

GOVERNMENT SPONSORSHIP

[0002] The present invention was developed in conjunction with the TexasDepartment of Transportation Research Project 0-2116 “Effects of Wet-MatCuring Time and Earlier Loading on Long-Term Durability of BridgeDecks.” As such, the Texas Department of Transportation may have rightsin the present invention.

TECHNICAL FIELD

[0003] The present invention relates, in general, to an apparatus andmechanism allowing near-immediate application of a protector mat for wetand/or elevated heat curing concrete surfaces. More specifically, theapparatus permits the automated addition of fluid, energy, and the likethroughout the entire curing process. The specific apparatus intends toimprove the curing process by creating ideal curing conditions thatresult in a more durable slab of concrete in a potentially shorteramount of time. “Rapid protection” equates to a reduced interval betweenplacement of fresh concrete to the time a protection system is securelyput in place. The present invention also relates to an improved methodfor affecting the curing of freshly-placed concrete.

BACKGROUND OF THE INVENTION

[0004] A concrete slurry is created by mixing water and concreteingredients, including cement and aggregates. The slurry begins toharden by a chemical reaction called hydration. While hydration occurs,the concrete is said to be “curing.” The curing conditions directlyfacilitate hydration and are essential to the realization of highquality concrete. For example, the curing conditions can impact theconcrete's durability, water tightness, strength, and resistance towear. In fact, proper curing techniques will improve nearly all thedesirable properties of concrete. Though concrete can cure for extendedperiods of time—perhaps even years—the most significant curing forlong-term durability occurs during the first few weeks after initialplacement. To ensure the hydration process extends until the concretebecomes as durable as practically and/or inherently possible, certaincuring protection measures are employed.

[0005] Maintaining the proper conditions for concrete curing requiresthe ability to satisfactorily control moisture content and temperaturelevels. Under proper conditions, the concrete will retain moisture as itcontinues to strengthen and harden during the curing process. Inaddition, improperly cured concrete will shrink to such an extent thatcracks can occur, damaging the strength and aesthetics of the finishedconcrete. Therefore, evaporation of mix-water from the concrete slurrymust be decreased or eliminated, as the retained moisture will alsoprevent the concrete from shrinking during drying. Unfortunately, aby-product of traditional curing construction methods has been longconstruction delays as the concrete slowly cures. Therefore, there is ademand and need for methods that can quickly cure concrete while stillremaining strong and durable.

[0006] Numerous techniques have been employed in order to accelerate thecuring process. For example, according to one technique, an electriccurrent has been conducted through the mix itself. More typical methodsinclude:

[0007] Water Cure—a concrete slab is flooded or mist sprayed in order toprevent mix-water evaporation. However, the process is time consumingand does not address potential problems with ambient conditions such asfreezing temperatures.

[0008] Water Retaining Methods—a covering (such as sand, straw, etc.) isplaced on the concrete and kept continuously wet. This method isineffective because the material can mar or become imbedded in the stillsoft concrete. Moreover, surface evaporation, poor temperatureconditions, and the inconsistent application of the material to theconcrete remain as problems.

[0009] Waterproof Paper or Plastic Film Seals—continuous layers orsheets are applied to the wet concrete surface to retain moisture.Again, the concrete has to be hard enough to resist surface damage. Theplastic films may also cause discoloration and can be problematic ifheat or energy needs to be applied to the concrete. A system does notcurrently exist that can quickly apply the layers to prevent surfaceevaporation.

[0010] Chemical Membranes—a chemical mixture, or ‘curing compound’, isadded to the curing concrete. The curing compound must be developed andused for specific concrete applications. This curing technique alonedoes not account for the need to control the temperature and moisturecontent of the curing concrete.

[0011] In addition to the various problems noted above, thesetraditional approaches have been deficient in producing an adequatefinal compressive strength. Also, the necessary apparatus can be toocostly or ineffective. An improved mechanism for curing concrete thatcan combine these approaches in an economical and timely manner isneeded.

[0012] The economics of curing are particularly important in regards tothe building of larger structures, such as pre-stressed beams and bridgedecks. Larger structures are built by casting the concrete in pre-madeforms or pouring the concrete on-site. In either case, the investment inmoney and man-hours is significant and reducing the time for curingincreases efficiency. Yet, the strength of the structure cannot becompromised for the sake of reducing production time.

[0013] While curing ensures a stronger concrete product, a smooth, hardsurface must also be achieved by subjecting the concrete to screeding.Historically, screeding was the process whereby a rigid piece of metalor wood was used to level the concrete and remove excess material. Atypical modem “screed machine,” as illustrated in FIG. 1, moves alongthe face of an uncured concrete structure on a set of rails. Freshconcrete is placed in front of the screed machine. The surface of thefresh concrete is unlevel and must be vibrated, smoothed, and finished(i.e., textured or grooved). For roadway and bridge deck applications,finishing is required for a smooth riding surface whiletexturing/grooving of the pavement is performed for vehicle tractioncontrol. The screed machine performs all of these functions at a rate ofapproximately twenty longitudinal feet per hour, depending on slabthickness, deck width, etc. A manned platform often follows the screedmachine. The platform operator adds a liquid curing compound and/orsprays water on the concrete. As mentioned, premature “drying” of theconcrete before the curing process is substantially complete can lead toexcessive shrinkage, cracking, and undesirable micro-structural featuresin the concrete. However, curing compounds are not very effective atsealing the concrete and the water is prone to surface evaporation.

[0014] In some instances, heavy wet mats or blankets are applied to theconcrete to retain moisture and facilitate curing. The wet mats areapplied as soon as possible but, in order to protect the finishedsurface of the concrete pour, these wet mats generally cannot be applieduntil three to four hours after the concrete is poured. Applying the matbefore the concrete had set would mar the concrete.

[0015] The problems with wet-mats are compounded by a current industrytrend toward more “high-performance” concretes, which typically requirea much shorter interval (e.g., less than fifteen minutes) between thetime of the concrete placement and the application of the wet mats. Theresult is that a more immediate and higher level of protection isrequired for the freshly placed concrete. However, the extremely shortinterval of time required for the placement of curing mats or the likecurrently makes it impossible to do without marring the surface of theconcrete. It is also possible that the immediate application of matsdirectly on top of the surface of the concrete could adversely influencethe long-term durability of the cured concrete.

[0016] Finally, heat, though desirable in cold weather concreting, israrely applied to the top surface of curing concrete due to practicaland logistical limitations with the current techniques for curing.However, with the use of more complex “high performance” concretes,there is a need to substantially shorten the interval between the timethe concrete is placed and the time heat is applied. The typicalinterval is currently around three to four hours. A process or mechanismthat shortened that interval would be desirable in many environments.

[0017] There currently exists a need for preventing moisture loss andsurface evaporation from finished concrete. In addition, in certainapplications, heat, chemicals, or water may also need to be added aftera protective mat is deployed. Present day seals or blankets cannot beapplied to concrete in a timely manner without marring the surface ofthe concrete and potentially weakening the finished product. Also, thetechnology does not exist to apply heat in a timely manner. Therefore, amechanism that facilitates the placement of wet mats and allows for theaddition of heat, water, chemicals, and the like is needed

SUMMARY OF THE INVENTION

[0018] For the first time, a curing protection system for concrete isaccomplished at a fraction of the time that it presently takes and in anefficient and relatively inexpensive manner.

[0019] Existing methods and structural arrangements are utilized, andmodifications introduced to effect the objective of shorter time spansfor the installation of the curing protection system over the concretewhile maintaining the quality of the concrete. Both a unique structureand method of proceeding are introduced by the present invention.

[0020] Curing mats, which are presently employed for curing concrete,are used according to the present invention, but in a modifiedstructural manner, resulting in the unique structure. The procedureaccording to which the curing mats are used is also modified, resultingin the unique method.

[0021] In essence, the unique structure allows the curing mats to beused in conjunction with the laying of the concrete but with a shorttime delay. The curing mats are positioned relative to the freshly laidconcrete but not in initial contact so that the surface quality of theconcrete is not affected, but curing is. Subsequent to a short delayduring which the application of moisture and/or a curing compound canproceed, contact of the curing mats with the concrete is made and apotentially more rapid curing takes place.

[0022] The present invention then, relates to a rapid protection systemfor freshly placed concrete to improve durability. In greater detail,and in a preferred embodiment of the invention, the present inventionemploys a screed machine where the screed machine and a curing compoundplatform currently used in the industry remain essentially the same. Thepresent invention follows the application of moisture or a curingcompound with the immediate placement of a mat to protect the curingcement. The invention rolls sections of curing mats along screed railsthat are already in place and leveled for the concrete placement screedmachine. The mats are suspended through the use of either 1) acollapsible, embedded structural system or 2) an attachable structuralsystem. Either system can be designed in a number of ways to allow themats to be rolled up rather compactly and also to span the deck surfaceof the concrete pad when rolled out. Once the mat is suspended acrossthe deck, water vapor, heat, chemicals, and the like may be applied.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following eight figures are chosen as representative of thevarious embodiments. The foregoing, and additional objects, features,and advantages of the present invention will become apparent to those ofskill in the art from the following detailed description of a preferredembodiment thereof, taken in conjunction with the accompanying drawings,in which:

[0024]FIG. 1 is a perspective view exemplary of a screed machine in-useon a concrete bridge deck;

[0025]FIG. 2 is a perspective view of a screed machine combined with therapid protection system in accordance with one embodiment of the presentinvention;

[0026]FIG. 3 is a cross section of a screed machine combined with therapid protection system in accordance with one embodiment of the presentinvention;

[0027]FIG. 3A is an exploded cross section of the rapid protectionsystem for freshly placed concrete in accordance with one embodiment ofthe present invention;

[0028]FIG. 4 is a perspective view of a screed machine with a deployedrapid protection system in accordance with one embodiment of the presentinvention wherein the typical curing compound platform is removed and aprotective mat is immediately deployed after a screed machine passesover freshly placed concrete;

[0029]FIG. 5 is a cross section of a screed machine with a deployedrapid protection system in accordance with one embodiment of the presentinvention wherein the typical curing compound platform is removed and aprotective mat is immediately deployed after the screed machine passesover freshly placed concrete;

[0030]FIG. 5A is an exploded cross section of the rapid protectionsystem for freshly placed concrete in accordance with one embodiment ofthe present invention;

[0031]FIG. 6 is a cross section of a collapsible truss in accordancewith one embodiment of the present invention;

[0032]FIG. 7 is a perspective view of a screed machine combined with therapid protection system using tensioned support wires to support aprotective mat in accordance with one embodiment of the presentinvention;

[0033]FIG. 8 is a cross section of a rapid protection system matsuspended over curing concrete in accordance with one embodiment of thepresent invention; and

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0034] While the invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those havingordinary skill in the art and access to the teachings provided hereinwill recognize additional modifications, applications and embodimentswithin the scope thereof and additional fields in which the presentinvention would be of significant utility.

[0035] Generally a curing compound is applied immediately after a screedmachine smooths the poured or placed concrete, followed much later bythe application of wet mats or some similar protector when the concretehas achieved sufficient strength to support that operation. The matsoperate to retain moisture in the concrete necessary for a number ofdesirable characteristics, including durability and the prevention ofcracks. However, this curing method has the significant disadvantage ofnot being able to provide moist curing when it is most neededimmediately after a curing compound is added. The result is significantmoisture loss for freshly placed concrete, especially under adverseconditions. In the case of high performance concretes with lowwater-cement ratios, the curing method may deny much needed moisture tothe concrete resulting in autogenous shrinkage and cracks.

[0036] The present invention is developed to retain and provide moisturefor curing much earlier than it is done under the conventional methods.It is a two-stage method where, in stage 1, a curing mat is suspended ona collapsible or attachable truss that will prevent it from damaging thestill “green” concrete. In this case, the mat is able to provide moreeffective sealing of the concrete than a curing compound would. Thus,nearly one-hundred percent humidity over the paved concrete can bemaintained. Further, the rapid protection system of the presentinvention can be placed on existing rails used by a screed machine, andit can be placed immediately after the paver has moved away from thepaved area.

[0037] In stage 2, the rapid protection system curing mat is lowered tothe slab when the slab is able to support the weight of the mat. Thiscould be earlier than the final setting time because constructionpersonnel do not have to get on the slab to place the mat. The quickplacement will enable the rapid protection system to provide additionalmoisture to prevent autogenous shrinkage of high performance concrete.The short interval of time between the paving of the concrete andplacement of the mat could double or triple the lifespan of the concreteslab or deck.

[0038] There are illustrated drawings wherein the numerals have beenused throughout the several views to designate the same or similarparts. FIG. 1 depicts a slab of curing concrete 10 with an affiliatedscreed machine 12. The dimensions of slab 10 and screed machine 12 are,of course, dependent upon the particular dimensions of the roadway,bridge deck, or other item being constructed. In any event, screedmachine 12 is disposed in operative position over concrete slab 10. Forthe purposes of illustrating the present invention, the item to beconstructed is a bridge deck consisting of an abutment 4 supportingsteel beams 6.

[0039] Screed machine 12 includes a main trusswork or frame 16 having afirst end 16 a and a second end 16 b. Frame 16 extends across and overthe surface of concrete slab 10. While not depicted here, screed machine12 can incorporate a texturing and/or grooving unit mounted on frame 16.In addition, means to vibrate and smooth slab 10 would be included andsuch means are well known in the art.

[0040] As commonly practiced, rough concrete 20 is placed upon theunfinished bridge deck. The slurry or rough concrete 20 is held in placeby forms 22. Screed machine 12 consists of screed frame 16, screed rails18 and a curing compound platform 24. Frame 16 rests on screed rails 18at a first end 16 a and second end 16 b. Rails 18 are preferably formedat the top of forms 22 or as a separate component along with forms 22.Frame 16 then progresses from a first end of slab 10 to a second end bymeans known in the art. Grooving, texturing and/or vibrating meansconvert rough concrete 20 into flat slab 10. Next, curing compoundplatform 24 passes along screed rails 18 behind screed frame 16. Anoperator stands on platform 24 in order to spray water and/or curingcompounds onto slab 10 to facilitate curing. Once the surface of slab 10has hardened for several hours, a wet mat 8 can be applied to thesurface of concrete slab 10 to prevent the evaporation of any moistureor curing compounds located in the slab 10 or on the surface thereof.

[0041] Turning now to a detailed description of the present invention,as illustrated in FIGS. 2-9, a rapid protection system for freshlyplaced concrete allows for a substantial decrease in the time intervalbetween concrete placement and mat and heat application. First, FIGS. 2and 3 show a screed machine 12 employing the principals of a rapidprotection system (‘RPS’) 14 of the present invention. RPS 14 includes aroller 30, a beam 32 holding a RPS mat 34, and a support structure (i.e.a truss 44). Mat 34, sized to cover slab 10, is pre-wound onto beam 32,which is supported by frame members 36 above slab 10. Frame members 36and a lead bar 38 are also parts of the RPS 14 support structure. Theillustrated frame members 36 are ‘A’ shaped and are supported by wheeledbases 52 that are adapted to move along screed rails 18. However, framemembers 36 supporting beam 32 could be shaped in a number of other ways.More important is the fact that beam 32 can move along slab 10 using thepre-existing screed rails 18. Therefore, mat 34 can be installed in atimely and cost effective manner.

[0042] In usage, mat 34 is unrolled from beam 32 and lead by lead bar 38toward slab 10. Ultimately, the unrolled mat 34 is secured to slab 10 ata first end and along the edges of slab 10. Specifically, hangers 26 arepositioned over screed rails 18. Support beam 32 is then rolled alongscreed rails 18 from a first end of slab 10 to a second end, i.e. alongand toward the direction of travel of screed machine 12. Mat 34 unrollsfrom roller 30. A series of collapsible hangers 26 in the form of atruss 44 (FIG. 6) support mat 34 above slab 10. Collapsible truss 44could either be attached to mat 34 and, therefore, truss 44 could“fold-down” as mat 34 is being rolled up. Then, as mat 34 is unrolled,each truss 44 would “fold-out.” A small amount of cross bracing could beincluded between adjacent truss hangers 26 once truss 44 is in anexpanded position. Another embodiment, referring to FIG. 3, would be tohave a second worker to the left of RPS mat roller 30. As mat 34 isbeing unrolled (in this case without hangers 26 embedded into the bigroll), a person attaches truss 44 hangers to mat 34.

[0043]FIG. 3 represents a cross view of one embodiment of the presentinvention and depicts a bridge deck represented by abutment 4 andsupporting steel beams 6. The concept of a bridge deck could be replacedby a roadway or any mostly horizontal item that requires a slab ofconcrete. Forms 22 retain the concrete poured onto the bridge deck whilescreed rails 18 rest on top of the form 22 as noted. Screed machine 12moves along screed rails 18. Curing compound platform 24 follows thesame direction of travel as screed machine 12. Next, roller 30 alsotravels along screed rails 18 and mat 34 is unwound from beam 32.

[0044]FIGS. 3a and 3 b illustrate heater and water outlet mechanismsintegrated into mat 34. The distance of mat 34 over slab 10 can varywith each application with a distance of two to four inches above thedeck for most applications. As mentioned above, additional water may benecessary to maintain the proper moisture content for the curingconcrete. Water outlet 42 allows for the continuous application of wateralong the entire length of concrete slab 10. In addition, a heater 40can be used in appropriate environments to either speed the curingprocess or prevent mix water from freezing during hydration. Of course,additional water from water outlet 42 could also freeze in someenvironments without heater 40.

[0045]FIG. 3a also shows in greater detail mat 34 suspended above aconcrete slab by means of hangers 26. Screed rails 18 are formed muchlike a steel rail for a train, so they are somewhat rounded at the top.Thus, hangers 26 for truss 44 simply “hang” over rail 18 at both edges.Protective mats cannot be directly applied to concrete for three to fourhours following screeding because the contact can potentially mar andweaken the final concrete product. Each hanger 26 has a mat loweringmechanism 38 (FIGS. 3a and 5 a). Though any number of methods could beemployed to lower mat 34 to the slab 10, including electric motors, asimple latch is illustrated in the figure. Once the concrete hashardened to a sufficient degree, mat 34 is lowered into direct contactwith slab 10. Unless grooving operations will be performed under mat 34later, truss 44 supports can be removed.

[0046] For extremely wide pours, the truss/hanger system may need to“spoke” into the concrete at certain locations. FIG. 6 demonstratesmeans whereby mat 34 is suspended by lightweight, collapsible truss 44.Truss 44 spans the width of slab 10 from a first form 22 to a secondform 22. A spoke 46 extends vertically into the concrete to supporttruss 44. Small diameter holes caused by spokes 46 would be sealed withgrout, epoxy or the like after the curing operation is complete and thelifespan of slab 10 would not be compromised. Another possible method tosuspend RPS mat 34, especially for extremely wide placements, would bethe use of tension support wires 48 as shown in FIG. 7. Tensioned wires48 assist in elevating mat 34 above slab 10. In FIG. 7, wires 48 areattached to the curing compound platform 24. However, they could beattached to other locations that are capable of providing the necessarysupport. Mat 34 lies on the wires after roller 30.

[0047]FIGS. 4 and 5 show a second embodiment of the present rapidprotection system for freshly placed concrete where the curing compoundplatform 24 has been eliminated from screed machine 12. High performanceconcretes are intended to cure and set quicker than typical concretes. Aprotective covering must be placed over the concrete almost immediatelyfollowing screeding. Mat 34 unwinds from beam 32 by passing over helperroll 50. Helper roll 50 is designed to layout mat 34 in front of thedirection of travel the roller 30. Mat 34 suspension would still beaffected by use of truss 44 (with or without spokes 46 depending onwidth of the placement) or wires 48.

[0048] Although the present invention has been described in terms of apreferred embodiment, it will be understood that numerous variations andmodifications may be made without departing from the invention. Thus, itis to be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedabove.

What is claimed is:
 1. A rapid protection system for freshly placedconcrete, comprising: a pair of elongated parallel extending supporttracks extending along the elongated, parallel edges of the freshlyplaced concrete; a mat extending the full width of the freshly placedconcrete and between the elongated parallel edges thereof; and means fordisplacing and positioning said mat along said elongated parallelextending tracks such that said mat is positioned above the top surfaceof the freshly placed concrete at a distance approximately 4 inchesabove the top surface of the freshly placed concrete.
 2. The rapidprotection system for freshly placed concrete as defined in claim 1,further comprising: a platform which extends between the elongated,parallel edges of the freshly placed concrete and is displaced alongsaid elongated parallel extending tracks in conjunction with thedisplacement and positioning of said mat such that the freshly placedconcrete can be treated in advance of the positioned mat above the topsurface of the freshly placed concrete.
 3. The rapid protection systemfor freshly placed concrete as defined in claim 1, further comprising: apair of elongated parallel extending forms adjacent to said supporttracks for defining the outer width limit of the freshly placedconcrete.
 4. The rapid protection system for freshly placed concrete asdefined in claim 3, wherein said support tracks are formed as part ofsaid forms, and are located as the top edge of said forms respectively.5. The rapid protection system for freshly placed concrete as defined inclaim 1, wherein said mat forms a roller supported on said supporttracks.
 6. The rapid protection system for freshly placed concrete asdefined in claim 5, wherein said means for displacing and positioningsaid mat comprises a pair of frame members situated on opposed ones ofsaid support tracks with said roller extending between and supported bysaid frame members.
 7. The rapid protection system for freshly placedconcrete as defined in claim 6, wherein said means for displacing andpositioning said mat comprises a feed bar which extends from said framemembers outwardly from said roller, the engagement of said mat with saidfeed bar effecting the positioning of said mat relative to the topsurface of the freshly placed concrete.
 8. A rapid protection system forfreshly placed concrete in conjunction with a screed machine, the screedmachine producing the freshly placed concrete, comprising: a pair ofelongated parallel extending support tracks extending along theelongated, parallel edges of the freshly placed concrete for supportingthe screed machine for displacement along said support tracks; a matextending the full width of the freshly placed concrete and between theelongated parallel edges thereof; and means for displacing andpositioning said mat along said elongated parallel extending tracks suchthat said mat is positioned upstream of the screed machine and above thetop surface of the freshly placed concrete at a distance approximately 4inches above the top surface of the freshly placed concrete.
 9. Therapid protection system for freshly placed concrete as defined in claim8, further comprising: a platform which extends between the elongated,parallel edges of the freshly placed concrete and is displaced alongsaid elongated parallel extending tracks in conjunction with thedisplacement of the screed machine and the displacement and positioningof said mat such that the freshly placed concrete can be treated inadvance of the positioned mat above the top surface pf the freshlyplaced concrete.
 10. The rapid protection system for freshly placedconcrete as defined in claim 8, further comprising: a pair of elongatedparallel extending forms adjacent to said support tracks for definingthe outer width limit of the freshly placed concrete.
 11. The rapidprotection system for freshly placed concrete as defined in claim 10,wherein said support tracks are formed as part of said forms, and arelocated as the top edge of said forms, respectively.
 12. The rapidprotection system for freshly placed concrete as defined in claim 8,wherein said mat forms a roller supported on said support tracks. 13.The rapid protection system for freshly placed concrete as defined inclaim 12, wherein said means for displacing and positioning said matcomprises a pair of frame members situated on opposed ones of saidsupport tracks with said roller extending between and supported by saidframe members.
 14. The rapid protection system for freshly placedconcrete as defined in claim 13, wherein said means for displacing andpositioning said mat comprises a feed bar which extends from said framemembers outwardly from said roller, the engagement of said mat with saidfeed bar effecting the positioning of said mat relative to the topsurface of the freshly placed concrete.
 15. A method for protectingfreshly placed concrete using a mat, comprising the steps of placing themat above the top surface of the freshly placed concrete such that saidmat is approximately 4 inches above the top surface; maintaining the matsuspended above the top surface of the freshly placed concrete for a setperiod of time; and placing the mat on the top surface of the freshlyplaced concrete after sid set period of time for a further set period oftime.
 16. The method for protecting freshly placed concrete as definedin claim 15, further comprising the steps of: forming the mat into aroller; supporting the roller above the top surface of the freshlyplaced concrete such that it extends along the fill width of the freshlyplaced concrete; and dispensing the mat to achieve said suspension. 17.The method for protecting freshly placed concrete as defined in claim16, further comprising the step of: releasing the mat after saidsuspension to effect said placement.